The present invention relates to a semiconductor integrated circuit device, and to, for example, a technology effective for application to one equipped with a step-down power circuit for stepping down an external power supply voltage and supplying it to an internal circuit.
With advances in semiconductor processing technology, progress has been made toward reducing the size of each MOSFET and the size of a memory cell. Owing to the reduction in device size, a drop in operating voltage of the MOSFET has been performed in terms of problems such as a short channel effect and hot carriers, etc. On the other hand, an external supply source voltage of a semiconductor integrated circuit device is determined by a source or power supply voltage of a system equipped therewith. It is difficult to reduce such a system power supply voltage in association with the device size reduction that has been put forward in the semiconductor integrated circuit device. As means for filling the gap left between the system power supply voltage and the operating voltage of each MOSFET formed in the semiconductor integrated circuit device, a step-down circuit is provided for the semiconductor integrated circuit device to thereby step down an external power supply voltage corresponding to the system power supply voltage so as to fit to each MOSFET constituting an internal circuit.
Such a negative feedback amplifier circuit (voltage follower circuit) as shown in FIG. 21 is used as the step-down circuit. It is considered that as shown in FIG. 22, a reference voltage Vref formed by a constant voltage generating circuit is inputted to the negative feedback amplifier circuit where it is power-amplified to form an output voltage Vout, after which it is supplied to a load circuit (internal circuit) Z typified by a parallel circuit made up of a resistor and a capacitor as an operating voltage. As other examples of amplifier circuits using MOSFETs, there are known, Unexamined Patent Publication Nos. Hei 11(1999)-284447, Hei 3(1991)-174811, Hei 5(1993)-252020, Hei 10(1998)-22749, etc.
It is particularly desirable that in a semiconductor integrated circuit device installed in a portable electronic apparatus, its current consumption is reduced as small as practicable. Thus, the semiconductor integrated circuit device equipped with the step-down circuit needs to reduce current consumption of the step-down circuit as small as possible. However, the above-described negative feedback amplifier circuit such as shown in FIG. 21 needs to cause a bias current of several hundreds of xcexcA to flow through the use of a current source I1a for the purpose of initializing an internal voltage. There may be cases in which, for example, a semiconductor integrated circuit device installed in a portable electronic apparatus needs to set current consumption at standby with no operation to about 0.5 xcexcA. A problem arises in that current consumption allowed for the step-down circuit to realize such low power consumption results in about 120 nA at most, and the step-down circuit cannot be installed in a semiconductor integrated circuit device intended for such low power consumption.
An object of the present invention is to provide a semiconductor integrated circuit device equipped with a negative feedback amplifier circuit or a step-down circuit which realizes stabilization of an output voltage effectively in response to a variation in power supply voltage. Another object of the present invention is to provide a semiconductor integrated circuit device equipped with a negative feedback amplifier circuit or a step-down circuit which implements enlargement of a source voltage operating range and stabilization of an output voltage. The above, other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.
Summaries of typical ones of the inventions disclosed in the present application will be described in brief as follows: A constant current source is used to cause a bias current for setting current consumption to flow in each differential amplifying MOSFET. A capacitor is provided between an external power supply voltage and a predetermined circuit node to thereby detect a reduction in the external power supply voltage. An operating current of the differential amplifying MOSFET is increased through the use of a current flowing in the capacitor due to such an external power variation, thereby executing the operation of stabilizing an output voltage corresponding to the reduction in the external power supply voltage.
Further, a constant current source is used to cause a bias current for setting current consumption to flow in each differential amplifying MOSFET. A capacitor is provided between a circuit node responsive to a variation in external power supply voltage, and a ground potential to thereby detect a rise in the external power supply voltage. An operating current of the amplifying MOSFET is increased through the use of a current flowing in the capacitor due to such a variation in external power supply voltage to thereby execute the operation of stabilizing an output voltage corresponding to the rise in the external power supply voltage.